Studies of benthic invertebrate biomass and periphyton biomass show that the densities of these benthic species are reduced by floods and increase exponentially after floods.

Instream habitat models predict water depths and velocities reasonably accurately and if appropriate suitability curves are used the models predict the potential benthic biomass at each point in the river. However, because flow and available habitat vary with time, the potential biomass is only reached after a long period of stable flow.

A conceptual model of benthic production has been developed for SEFA (System for Environmental Flow Analysis software program)  to predict the effect of flow regime on benthic biomass. This models hydraulic conditions (velocity, shear stress, dimensionless shear stress, substrate stability, habitat suitability) at each point in the river and estimates how these influence the abundance of benthos (e.g., periphyton or benthic invertebrates) at the point. The processes that are modelled are population growth through immigration/reproduction, population loss through emigration/mortality, and population movement within the reach as habitat suitability changes.

The benthic growth process comprises two mechanisms, colonisation through drift of invertebrates or plant cells from upstream sources and growth through population increase.

The conceptual model  produces realistic results and will be useful in comparing the effects of changing the flow regime of a river on benthic communities.